Annular airborne vehicle

ABSTRACT

An airborne vehicle having a wing-body which defines a wing-body axis and appears substantially annular when viewed along the wing-body axis, the interior of the annulus defining a duct which is open at both ends. A propulsion system is provided comprising one or more pairs of propulsion devices, each pair comprising a first propulsion device mounted to the wing-body and positioned on a first side of a plane including the wing-body axis, and a second propulsion device mounted to the wing-body and positioned on a second side of the plane including the wing-body axis.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Divisional of copending U.S. application Ser. No.12/594,719, filed Oct. 5, 2009, which is a U.S. nationalization under 35U.S.C. §371 of International Application No. PCT/GB2008/001329, filedApr. 16, 2008, which claims priority to United Kingdom application no.0707512.0, filed Apr. 18, 2007. The disclosures set forth in thereferenced applications are incorporated herein by reference in theirentireties.

The present invention relates to an annular airborne vehicle—that is, avehicle having an outer wing-body which defines a wing-body axis andappears substantially annular when viewed along the wing-body axis, theinterior of the annulus defining a duct which is open at both ends.

It is well understood that aircraft should be designed for minimal dragand mass characteristics, while maximising lift and aeroelasticcharacteristics so that fundamental aircraft design parameters may beadapted to achieve specific goals including better lift to drag ratios,better fuel efficiency, longer endurance and higher payload capacities,for example.

These fundamental design goals remain true whether the aircraft might bea miniature unmanned air vehicle (UAV), or a glider, or a passengeraircraft, or indeed a large transport aircraft.

It is an objective in many UAV applications to provide means for shorttake off and landing (STOL) or vertical take off and landing (VTOL), sothat devices may be deployed and recovered without difficulty whenrunways may not be available. It is also desirable for UAVs to includemeans to hover, where surveillance, localisation, or communicationsactivities may be required with little or no aircraft motion relative tothe ground. Under such scenarios it is also desirable that the UAVshould be capable of transition into an efficient forward flight phase,and vice versa, so that vehicle endurance would not necessarily becompromised by flight inefficiencies during VTOL, STOL, or hover phases.Under some circumstances it is advantageous to deploy such UAVs not onlyfrom ground but also from aircraft which may already be in flight, orland vehicles which may themselves be in motion, and therefore such UAVswould require special capabilities in order to withstand the demandingconditions imposed by such deployment envelopes.

Large UAVs are used in high altitude, long endurance scenarios wherereconnaissance, or surveillance or imaging or communications functionsmay be required in order to achieve mission goals. Under such scenariosthe endurance characteristics of the UAV become more important than takeoff or landing aspects, where lift to drag ratios must be high, massmust be low, and strength to weight ratios must also be high. It followsfrom aerodynamic principles that induced drag may be minimised byincreasing the aspect ratio (AR) of the wing, where:AR=B ² /S(B=span; S=projected planform area)which produces long slender wings where maximal efficiency must bebalanced with aeroelastic constraints where wing structures must alsosurvive other stresses induced during severe weather or take off orlanding. Therefore such UAVs require improved vehicle forms in order todeliver better performance in terms of endurance, or range, or fuelefficiency, or payload capacity.

Therefore it is an object of this invention to disclose a common annularair vehicle form that may be utilised efficiently across a variety ofUAV applications including those based upon miniature, agile vehicles,and large high altitude long endurance vehicles, and gliders.

It is also another object of this invention to disclose a common annularair vehicle form that may be utilised efficiently across a variety ofmanned aircraft applications including those based upon glider, lighttransit, heavy transit and passenger aircraft.

A first aspect of the present invention provides an airborne vehiclehaving a wing-body which defines a wing-body axis and appearssubstantially annular when viewed along the wing-body axis, the interiorof the annulus defining a duct which is open at both ends; and apropulsion system comprising one or more pairs of propulsion devices,each pair comprising a first propulsion device mounted to the wing-bodyand positioned on a first side of a plane including the wing-body axis,and a second propulsion device which is mounted to the wing-body,positioned on a second side of the plane including the wing-body axis,and operable independently of the first propulsion device.

Preferably a direction of thrust of the first propulsion device can beadjusted independently of the direction of thrust of the secondpropulsion device, for instance by rotating the propulsion device.Alternatively each propulsion device comprises a thrust generator and aplurality of ducts arranged to receive propulsion gas from the thrustgenerator, and the direction of thrust of each propulsion device can beadjusted independently of the direction of thrust of the otherpropulsion device by adjusting the flow of propulsion gas in the ducts.In this case typically each duct is contained within the wing-body andat least some of the ducts have an inlet and an outlet in the wing-body.

In certain embodiments a thrust vector of each propulsion device can beadjusted between a first configuration in which the thrust vectors areco-directed and a second configuration in which the thrust vectors arecontra-directed.

In one embodiment of the first aspect of the invention a magnitude ofthrust of the first propulsion device can be adjusted independently ofthe magnitude of thrust of the second propulsion device, but not thedirection of thrust.

Thus in general terms the propulsion devices are operable independentlyin the sense that either the direction of thrust of the first propulsiondevice can be adjusted independently of the direction of thrust of thesecond propulsion device; or a magnitude of thrust of the firstpropulsion device can be adjusted independently of the magnitude ofthrust of the second propulsion device; or both.

Preferably a controller device is provided which is configured toindependently operate the propulsion devices by issuing respectivecontrol signals to the propulsion devices.

A second aspect of the invention provides an airborne vehicle having awing-body which defines a wing-body axis and appears substantiallyannular when viewed along the wing-body axis, the interior of theannulus defining a duct which is open at both ends, wherein thewing-body appears swept forward when viewed from a first viewing angle,and swept backward when viewed from a second viewing position at rightangles to the first viewing angle.

In certain embodiments of the invention, the double-swept configurationof the second aspect of the invention provides several advantages:

-   -   it enables the center of gravity of the annular vehicle to be        more easily separated from its center of pressure, and therefore        provides for better static and dynamic margins in pitch        stability;    -   aeroelastic forces which would otherwise subject conventional        planar forwardly swept wings to excessive tensile or flutter        loads are effectively braced and dampened by the resilient        annular structure of the wing-body;    -   the element of forward sweep makes the vehicle more tolerant of        relatively high angles of attack, with lower susceptibility to        stall, which is important when executing landings, take-off or        other manoeuvres;    -   the element of forward sweep improves lift over drag ratios        under some circumstances.

Preferably the wing-body has a leading edge with two or more noses, anda trailing edge with two or more tails which may be rotationally offsetin relation to the noses (for instance by 90 degrees).

Typically at least part of the leading and/or trailing edge of thewing-body follows a substantially helical curve.

A third aspect of the invention provides an airborne vehicle having awing-body which defines a wing-body axis and appears substantiallyannular when viewed along the wing-body axis, the interior of theannulus defining a duct which is open at both ends, wherein thewing-body carries at least one rudder on its left side and at least onerudder its right side.

In some embodiments the wing body carries two or more rudders on itsleft side and two or more rudders on its right side, and the wing-bodyis formed with a slot between each adjacent pair of rudders.

Preferably the wing-body has a projected planform area S, and a maximumouter diameter B normal to the wing-body axis, and wherein the ratioB²/S is greater than 0.5. The relatively large diameter wing-bodyenables an array of two or more sensors to be well spaced apart on thewing-body, providing a large sensor baseline. In this way the effectiveacuity of the sensor array increases in proportion to the length of thesensor baseline. Also, the relatively high ratio B²/S gives a high ratioof lift over drag, enabling the vehicle to be operated efficiently as aglider.

The duct may be fully closed along all or part of its length, orpartially open with a slot running along its length. The duct may alsoinclude slots or ports to assist or modify its aerodynamic performanceunder certain performance conditions.

Various embodiments of the invention will now be described by way ofexample with reference to the accompanying drawings, in which:

FIG. 1 a is a front view of a first propelled vehicle;

FIG. 1 b is a cross-section of the right-hand side of the vehicle takenalong the wing-body axis and along a line A-A in FIG. 1;

FIG. 1 c is a cross-section of the right-hand side of a second propelledvehicle, where its propellers are located within the forward half of theduct;

FIG. 2 a is a cross-section of the right-hand side of a third propelledvehicle taken along the wing-body axis and along a line B-B in FIG. 2 b,where its propellers are located within the rearward half of the duct;

FIG. 2 b is a plan view of the third propelled vehicle;

FIG. 2 c is a cross-section of the right-hand side of a fourth propelledvehicle taken along the wing-body axis and along a line C-C in FIG. 2 d,where its propellers are located within the forward half of the duct;

FIG. 2 d is a plan view of the fourth propelled vehicle;

FIG. 3 a is a front view of the fourth propelled vehicle with itspropellers in an up thrust configuration;

FIG. 3 b is a cross-section of the right-hand side of the fourthpropelled vehicle taken along the wing-body axis and along a line D-D inFIG. 3 a;

FIG. 3 c is a front view of the fourth propelled vehicle with itspropellers in a contra-directed spin thrust configuration;

FIG. 3 d is a cross-section of the right-hand side of the fourthpropelled vehicle taken along the wing-body axis and along a line D-D inFIG. 3 c;

FIG. 4 a is a front view of a fifth propelled vehicle with itspropellers in a forward thrust configuration and located behind therearward half of the duct;

FIG. 4 b is a cross-section of the right-hand side of the fifthpropelled vehicle taken along the wing-body axis and along a line E-E inFIG. 4 a;

FIG. 4 c is a cross-section plan view of the fifth propelled vehicletaken along a line F-F in FIG. 4 a;

FIG. 5 a is a front view of a sixth propelled vehicle with itspropellers mounted conformally within the annular wing body;

FIG. 5 b is a cross-section of the right-hand side of the sixthpropelled vehicle taken along a line G-G in FIG. 5 a;

FIG. 5 c is a rear view of the vehicle of FIG. 5 a;

FIG. 5 d is an underside view of the vehicle of FIG. 5 a;

FIG. 6 a is a front view of a glider;

FIG. 6 b is a cross-section of the right-hand side of the glider takenalong the wing-body axis and along a line H-H in FIG. 6 a;

FIG. 6 c is a plan view of the glider;

FIG. 7 a is a front view of a seventh propelled vehicle;

FIG. 7 b is a side view of the vehicle of FIG. 7 a; and

FIG. 7 c is a plan view of the vehicle of FIG. 7 a.

Referring to FIGS. 1 a and 1 b, an airborne vehicle 1 has an outerwing-body 2 which is evolved from a laminar flow aerofoil profile (shownin FIG. 1 b) as a body of revolution around a wing-body axis 3. Thus theouter wing-body 2 appears annular when viewed along the wing-body axisas shown in FIG. 1 a. An inner wall 4 of the annulus defines a duct 5which is open fore and aft so that air flows through the duct as thevehicle moves through the air, generating aerodynamic lift bydifferential fluid flow across upper and lower aerofoil surfaces, whichin this example arises whenever the axis of the annulus maintains anangle of incidence to its trajectory.

As shown in FIG. 1 b, the aerofoil profile tapers outwardly graduallyfrom a narrow nose end 6 to a widest point 7, then tapers inwardly morerapidly to a tail end 8. In this particular embodiment the widest point7 is positioned approximately two-thirds of the distance between thenose and tail ends. The particular aerofoil section as described hassymmetrical upper and lower surfaces which in this example provides forlow minimum drag under cruising conditions, and may be modified invariants of this and other vehicles so as to modify the coefficients oflift, drag and pitch moment to suit the particular mission envelope andassociated fluid flow regime as determined by the relevant range ofReynolds numbers.

A pair of propulsors 9, 10 are mounted symmetrically on opposite sidesof a vertical plane containing the wing-body axis 3. In this particularembodiment the propulsors are shown as ducted electric fan motorscomprising propellers (or impellers) 11, 12 which are mounted onL-shaped support shafts 13, 14 which in turn are mounted to thewing-body in line with the widest point 7 as shown in FIG. 1 b. Thepropellers are mounted within shrouds 15, 16 in such a way that theirefficiency is increased within a proportion of the motor operatingenvelope. Each L-shaped shaft is pivotally mounted to the wing-body sothat it can rotate independently of the other shaft by 360 degreesrelative to the wing-body about an axis parallel to the pitch axis ofthe vehicle, thus providing thrust-vectored propulsion. Both the shroudand L-shaped shaft have an aerofoil section using a ratio between chordlength and height similar to that described for the outer wing-body,where the optimal relationship between height and chord is once againdetermined by the relative fluid flow regime as described by therelevant Reynolds number for these elements. Thus for example thepropulsors 9, 10 can be rotated between the co-directed configurationshown in FIGS. 1 a and 1 b, in which they provide a thrust force topropel the vehicle forward and along the wing-body axis, to acontra-directed configuration (not shown) in which they cause thevehicle to roll continuously around the wing-body axis.

The vehicle uses four independently operable motors (not shown) withinits propulsion system: two brushless DC electric motors to drive thepropellers, and two DC electric brushless motors to drive the L-shapedsupport shafts upon which the propeller motors are mounted, where amechanical worm drive gear reduction mechanism is used to transfer driveand loads between the motor and the L-shaped shafts. Alternative motortypes such as stepper motors may be used for the latter scheme, so longas operating loads are consistent with the rating of the motors.Similarly alternative motor types may be adopted for the propulsors,including internal combustion, gas turbine or solid propellant motors.

The thrust-vectored propulsors provide the means for motion along thewing-body axis, either forward or in reverse, and spin or roll aroundthe wing-body axis, and pitch or yaw about the vehicle's centre ofgravity (CofG), which in this embodiment is located below the wing-bodyaxis, above the lower annulus section, within a vertical plane thatcontains the wing-body axis, and approximately at 15 to 23% of the chordlength when measured from the nose. As described earlier it is clearthat the two propulsors may be contra-directed in order to inducevehicle roll. The two propulsors may also be co-directed. For instancewhen both are directed down so that their thrust vectors lies above theCofG, then the vehicle will pitch nose down. Similarly when the twopropulsors are directed up so that their thrust vector lies below theCofG, then the vehicle will pitch nose up. It is also clear that varyingdegrees of propulsor pitch in relation to the vehicle and each other maybe used to achieve vehicle pitch, roll and yaw. Yaw may also be inducedby differential thrust application when differential propellerrevolution rates are adopted. Thus it can be seen that the vehicle isable to dive, turn, roll and climb under its own autonomous control,since the vehicle also includes a controller device that includes themeans to measure linear accelerations in three orthogonal axes, andangular accelerations in three orthogonal axes, and processing methodsto calculate the control demands that would be delivered to thepropulsion system.

Thus the direction of thrust of the propulsor 9 can be adjusted by thecontroller device independently of the direction of thrust of thepropulsor 10 by issuing control signals to the electric motors whichdrive the L-shaped support shafts. Also, the magnitude of thrust of thepropulsor 9 can be adjusted by the controller device independently ofthe magnitude of thrust of the propulsor 10 by issuing control signalsto the electric motors which drive the propellers.

The vehicle has a high degree of manoeuvrability, since its thrustvectored propulsion may be arranged for high turn rates under dynamiccontrol. It is also clear that the vehicle has a high degree ofstability. In the first instance when motion is along the axis of thewing-body then relatively high speeds may be achieved withcontra-rotating propellers that cancel induced torque, whilecontra-directed propulsors provide for further roll stability. In thesecond instance when spin motion around the wing-body axis is induced,then angular momentum is increased and once again the stability of thevehicle is increased, where this may be measured as a reduction invehicle attitude or position errors when subject to external forces.

A significant advantage offered by this propulsion system is theprovision of effective attitude control at slow speeds, when alternativecontrol surfaces would be much less effective. It follows therefore thatlarge thrust vector demands may be used effectively at slow speeds, andduring launch or recovery, or take off and landing, while low thrustvector demands would satisfy the majority of performance envelopedemands when traveling at speed. Another significant advantage of thisarrangement is the relative ease with which the vehicle may transitionfrom launch to forward transit, or to hover, or VTOL/STOL, and viceversa. A further significant advantage of this arrangement is the lowdrag characteristic of the annular wing-body, which preferentiallyallows for high speed transit in normal forward flight.

The nose of the vehicle carries a pair of video cameras 17, 18 forcollision avoidance and imaging applications. The relatively largediameter of the wing-body enables the cameras to be well spaced apart,thus providing a long stereoscopic baseline that provides for accuraterange estimation by measurement of parallax between objects locatedwithin both camera fields of view. An ultrasonic transmitter 20 and tworeceivers 21, 22 are provided for acoustic imaging and sensing. Again,the wide baseline is an advantage since localization accuracy will beimproved by differential time of flight processing between the separatedreceivers. The outer wing-body 2 contains an interior space which can beseen in FIG. 1 a. This outer wing-body is preferentially manufacturedfrom a stiff composite material using glass or carbon fibre filamentslaminated alternately between layers of epoxy resin. Alternatively acheaper, less resilient wing-body may be moulded from a suitable hardpolymer such as polyurethane or high density polyethylene. Under certainconditions where mass reduction is paramount then the outer wing-bodyskin may be formed instead from a tough polymer film such as mylar. Itis also possible to manufacture the outer wing-body from aluminium,should the wing-body be pressurised. The interior space may bepressurized, and houses a pair of battery packs 21, 22, a pair of tailsensors 23, 24, and four toroidal vessels 25-28 spaced apart along thewing-body axis. The vessels may contain the vehicle electronics, somepropulsion sub-system elements and other items, and are joined by axialor tri-lateral struts (not shown) which would share the constructionmethods adopted for the toroidal vessels. In this particular embodimentthe toroidal vessels are preferentially manufactured from stiffcomposites using either glass or carbon fibre filaments wound helicallyaround the toroid and alternately laminated between layers of epoxyresin. Alternatively the toroidal vessels may be manufactured from asuitable grade of metal such as aluminium, stainless or galvanizedsteel, or titanium. The toroidal and annular structures disclosed hereinare designed to provide for superior aeroelastic resilience around thewing-body so that mass may effectively and safely be reduced withoutrisk of major stress loading or concentration at any section of theannulus.

The aspect ratio (AR) of the annular wing-body is defined as follows:AR=2B ² /Swhere B is the span of the wing-body (defined by the maximum outerdiameter of the wing-body) and where S is the projected planform area ofthe wing-body.

In the vehicle of FIG. 1 a, the AR is approximately 2, although thisnumber may be modified in other embodiments where the application maydemand other ratios. It is evident that the vehicle form may be adjustedby simple variation of its toroidal diameter to reflect narrow vehicleswhere aspect ratio is low, or to reflect broad vehicles where aspectratio is high. In either case specific advantages may be gained undercertain circumstances, since relatively high coefficients of lift may beachieved using a toroidal form with low aspect ratio, while optimalglide slope ratios, or equivalent ratios of lift over drag may beachieved using a toroidal form with high aspect ratio.

In the embodiment of FIGS. 1 a and 1 b, the propulsion devices aremounted towards the tail of the vehicle—that is towards the right-handside of FIG. 1 b. In the second embodiment shown in FIG. 1 c thepropulsion devices are mounted towards the nose of the vehicle—that istowards the left-hand side of FIG. 1 c. The front view of the vehicle ofFIG. 1 c is identical to that of the vehicle of FIG. 1 b.

A swept-wing vehicle is shown in FIGS. 2 a and 2 b. The front view ofthe vehicle of FIGS. 2 a and 2 b is identical to that of the vehicle ofFIG. 1 b.

The leading edge 30 of the wing-body of the vehicle describes a form ofhelical curve around one quadrant of the circumference of the wing body,where such a helix subtends an angle +θ with a vertical line 3 _(y)perpendicular to the wing-body axis 3, when viewed in elevation as shownin FIG. 2 a. This helical curve is used identically around the thirdquadrant of the circumference of the wing-body leading edge, while itsmirror image is used to form the second and third quadrants of theleading edge. The four helical elements are joined, so that the leadingedge forms a closed double chevron sweep around the forwardcircumference of the wing-body. Within this particular embodiment, thetrailing edge forms an identical closed double chevron sweep which istranslated along the axis 3 by the chord length of the aerofoil. Inother embodiments the relationship between the leading and trailingdouble chevron sweeps may be modified, for example to vary therelationship between orthogonal lift and rudder stabilization surfaces.

Similarly the trailing edge 31 of the wing-body of the vehicle subtendsa positive angle (not labeled) with the line 3 _(y). Thus, because themid-chord line of the wing-body (that is, a line at the mid-pointbetween the leading and trailing edges) subtends a positive angle withthe line 3 _(y) on both the upper and lower sides of the wing-body, thewing-body appears swept backward when viewed in elevation. In contrast,the leading edge 30 of the wing-body of the vehicle subtends an angle −θwith a horizontal line 3 _(x) perpendicular to the wing-body axis 3,when viewed in plan as shown in FIG. 2 b. Similarly the trailing edge 31of the wing-body of the vehicle subtends a negative angle (not labeled)with the line 3 _(x). Thus, because the mid-chord line of the wing-body(that is, a line at the mid-point between the leading and trailingedges) subtends a negative angle with the line 3 _(x) on both the leftand right-hand sides of the wing body, the wing-body appears sweptforward when viewed in plan.

The sweep angle δ is described in FIG. 7 c (and also labelled withnumeral 69) under an alternative embodiment and may vary between 0 to60°, and 0 to −60°, where δ is defined as the angle subtended by thehelix H_(xy) (i.e., the mid-chord line of the wing-body) and any planewhich lies normal to the axis of the annular wing-body, and where δ istranscribed by the mid-chord line around the annular wing-body, andwhere S is constrained by the axial displacement t1 between the twochords whose tangential planes are vertical (i.e., left and right sides)in relation to the chords whose tangential planes are horizontal (i.e.top and bottom sections). In this example and other embodiments the meanvalue of δ may be determined within each of four quadrants bounded bytwo orthogonal planes that coincide with the wing body axis 3, at whichboundaries 5 becomes zero. The axial displacement t1 is greater than orequal to 0.1 times the chord of the annulus. These relationships aredescribed again in FIG. 7 c.

In the embodiment of FIGS. 2 a and 2 b, the propulsion devices aremounted towards the tail of the vehicle—that is towards the right-handside of FIGS. 2 a and 2 b. In the embodiment shown in FIGS. 2 c and 2 d,the propulsion devices are mounted towards the nose of the vehicle—thatis towards the left-hand side of FIGS. 2 c and 2 d. The front view ofthe vehicle of FIGS. 2 c and 2 d is identical to that of the vehicle ofFIG. 1 b.

FIGS. 3 a and 3 b illustrate the vehicle of FIGS. 2 c and 2 d with itspropellers in an up thrust configuration, and FIGS. 3 c and 3 dillustrate the vehicle of FIGS. 2 c and 2 d with its propellers in acontra-directed spin thrust configuration.

FIGS. 4 a-4 c show a variant of the vehicle of FIGS. 2 a and 2 b.Whereas the wing-body in the vehicle of FIGS. 2 a and 2 b is sweptforward when viewed in plan, the wing-body in FIGS. 4 a-4 c is sweptbackward when viewed in plan. In this configuration the static anddynamic pitch stability margins are reduced by comparison with thewing-body scheme described in FIG. 2, however the propulsors havegreater degrees of freedom in thrust vector control with lowerinterference to lifting surface fluid flows. As a consequence thisscheme offers further improvements in vehicle agility.

FIG. 5 a is a front view of a sixth propelled vehicle, employing aconformal propulsion system. A starboard propeller (or impeller) 40 ismounted in the inlet port 44 of a starboard main duct 42 which runsalong the starboard side of the hull to a main outlet port 45, and aport propeller 41 (or impeller) is mounted in the inlet port of a portmain duct 43 which runs along the port side of the hull to a main outletport (not shown).

The ducting network of the propulsion system is symmetrical, so only thestarboard elements will be described in detail with reference to FIG. 5b. The starboard main duct 42 is coupled to a forward duct 46 at aninlet 47, and to a rear duct 48 at an inlet 49. The forward duct 46 hasport and starboard underside outlet ports 52, 50 in the underside of thehull, and the rear duct 48 has port and starboard underside outlet ports53, 51 in the underside of the hull.

The port main duct 43 is also coupled to the ducts 46, 48 via inlets(not shown) on the port side of the vehicle, similar to the inlets 47,49.

Note that all of the ducts described above are contained within theannular wing-body.

Valves (such as butterfly valves or sliding plate valves) are providedin the inlets 47, 49 (and the equivalent inlets on the port side of thevehicle), in the underside outlet ports 50-53, in the main outlet port45 (and the equivalent main outlet port on the port side of thevehicle), and in the forward and rear ducts 46, 48 between the port andstarboard underside outlet ports. The valves may be opened and closeddigitally by pulse width modulation control.

The valves can be operated independently to adjust the flow ofpropulsion gas in the ducts, and thus adjust the magnitude and directionof the thrust generated by the port and starboard propulsion systems.For example forward thrust can be achieved by closing the valves in theinlets 47, 49 (and the equivalent inlets on the port side of thevehicle), and opening the valves in the port and starboard main outletports. VTOL, STOL, or hover phases can be achieved by closing (fully orpartially) the valves in the port and starboard main outlet ports, andopening all other valves.

The underside outlet ports 50-53 are arranged to enclose a vertical axisthat locates the centre of gravity (CofG) of the vehicle within ahorizontal frame of reference. Therefore during VTOL, STOL or hoverphases the propellers, motors, ducts, and valves may be controlled by asuitable device so that thrust may be adjusted between the four ports50-53 in such a way that vehicle attitude and resultant vehicleaccelerations and velocities may be precisely controlled.

This controller device is described above for earlier variants of thisannular wing-body. Once again the embodiment is particularly describedwith ducted electric fan motors, although these may be replaced bysuitable alternative motors including internal combustion, gas turbine,or solid propellant motors.

A glider vehicle is shown in FIGS. 6 a-c. The wing-body of the vehiclehas an annular construction as shown in FIG. 6 a, and adopts a forwardlyswept shape similar to the wing-body of FIGS. 2 a and 2 b. The wing-bodyuses similar construction, and houses various sensors, battery packs,and toroidal vessels in common with the vehicles shown in FIGS. 1-4.

Because the glider has no propulsion devices, it has a fully conformalouter shape with no superstructure either inside the duct or projectingfrom the exterior of the vehicle, other than its two elevators 32, 33and two rudders 30, 31 which are conformally and orthogonally mountedaround the rear of the wing-body. The elevators and rudders are securedto the wing-body by linkage mechanisms that provide for rotation withinarcs of +/−30°. The elevators and rudders are controlled by worm drivemechanisms as disclosed for propulsor controls in FIGS. 1 to 5.

FIGS. 7 a-7 c show a propelled vehicle according to a further embodimentof the invention. As described for vehicles disclosed in FIGS. 2 to 6,this particular embodiment of the annular wing-body also includes wingsweep, and in particular a symmetrical double chevron sweep as explainedfor the vehicles described in FIG. 2, only in this embodiment the sweepangle δ 69 is approximately 21 degrees.

The vehicle has a twin propulsion system 70, 71 similar to that shown inFIGS. 2 a/2 b although in this particular embodiment the motors aremounted on the lower half of the annulus. Also, in contrast to thepropulsion system of FIGS. 2 a/2 b (in which the direction and magnitudeof thrust of each propulsion device can be adjusted independently of thedirection and magnitude of thrust of the other propulsion device) vectorcontrol actuation elements are not included in the embodiment of FIGS. 7a-7 c so in this case only the magnitude of thrust of each propulsiondevice can be adjusted independently of the magnitude of thrust of theother propulsion device, and not the direction of thrust (other than byswitching between forward and reverse modes). Note also that in afurther embodiment (not shown) the propulsion system of FIGS. 2 a/2 bmay be fitted to the vehicle of FIGS. 7 a-7 c.

The position of the motors around the annulus may be adjustedsymmetrically about the vertical plane that contains the wing-body axis,where absolute thrust vectors would need to be aligned to best fit therange of flight regimes intended. Elevators 74, 75 and ailerons 72, 73are included on the upper cambered wing-body section, while elevators78, 79 and ailerons 76, 77 are included on the lower cambered wing-bodysection, and rudders 80 to 82 are included on the left side of thewing-body, while rudders 83 to 85 are included on the right side of thewing-body. The form of this annular vehicle is particularly suited tolarge, high endurance platforms which seek to minimize mass and maximizeoperational efficiency and where agility concerns would not be soprevalent. Once again the annular wing-body form seeks to maximize abroad range of performance criteria including resilience to aeroelasticloading which become more dominant when aspect ratios become large.

In contrast with the circular annulus shown in FIG. 1 a, the annulus iswider than it is tall, as shown in the front view of FIG. 7 a. In thisembodiment the relationship between span B and chord is 8 to 1, whilespan B to wing-body height H is 5 to 1. The aspect ratio of thisembodiment is derived from:AR=2B ² /S

-   -   Where AR=16

This particular aspect ratio is suited to long endurance operationswhere efficient soaring will be required.

The wing-body is arranged as four cambered sections 94 to 97 joined byfour curved elements 90 to 93 that provide both for structural bracingand conformal housing of twin motors, fuel, batteries, undercarriage,control systems, stowage bays and payload items. The construction of thewing-body follows the methods and materials described for the earlierwing-bodies of FIGS. 1 to 6, where composite technologies would be usedextensively within its structures. Similarly the motors may be basedupon ducted electric fan, or internal combustion, or gas turbinetechnologies in either of push or pull configuration, augmented byhybrid energy sources including photovoltaic and fuel cell technologies.

The wing-body vehicle has three undercarriage elements 40 for providingstability during take-off and landing operations. Two elevator and twoaileron elements 72 to 79 are included on each of the upper and lowersections of the annular wing-body, where the linkage mechanism thatsecures these elements is similar to that disclosed for the vehicle formdescribed in FIG. 6 b, while its control mechanism uses a worm drive asdisclosed for vehicle forms disclosed in FIGS. 1 to 6. A plurality ofrudder elements 80 to 85 are arranged at either vertical side of theannulus, using a linkage mechanism similar again to that described inFIG. 6 b, and a control mechanism based again upon a worm drive asdisclosed for vehicle forms described in FIGS. 1 to 6, together withflared slots 86 to 89 between each adjacent pair of rudders whichprovide for longitudinal separation r₂ between each rudder element wherethe ratio S_(r) between the separation distance τ₂ and the mid-chordlength of the rudder element C_(mr) may vary between 0.5 and 5, suchthat:S _(r) =t2/C _(mr)and where the vertical height H_(sr) subtended by the slots may varybetween 0.3 and 0.8 times the height H of the annulus. Each rudderelement incorporates an appropriate aerofoil to ensure smoothaerodynamic flow along their discrete surfaces, where the preciseaerofoil shape would be similar to that adopted for the other sectionsof the annular wing body, with adjustments as might be necessary for thevariation in Reynolds number associated with rudder chord reduction.

In this particular embodiment three rudder elements 80 to 82 and 83 to85 are shown on each of left and right sides of the annular wing-body,and two flared slots 86, 87 and 88, 89 are also shown between the rudderelements on each of left and right sides. Each rudder houses a securelinkage that bonds with upper and lower wing-body sections to ensurestructural integrity, and to allow for rotation within a prescribed arcabout a vertical axis, where the arc would normally be constrained toless than ±30°.

In this embodiment of the annular wing-body the combination of annulus,slots and multiple rudders serve to minimise induced drag, parasiticdrag, mass and cross-flow effects for the whole of the annual wing-bodyvehicle while providing for stability and control in yaw. The doublechevron sweep configuration also improves the soaring capability of theannular wing-body, where lift over drag ratios are increased by theeffective forward sweep of upper and lower cambered lifting sections ofthe annular wing-body.

The high rotational symmetry of many of the wing-body shapes (as viewedalong the wing-body axis) described herein gives other advantages wherethe vehicle is to be operated in a continuous or transient roll mode.However, the invention also covers alternative embodiments of theinvention (not shown) including:

-   -   embodiments in which the duct is divided into two or more        separate ducts by suitable partitions    -   embodiments in which the outer wing-body itself defines two or        more separate ducts    -   embodiments in which the outer wing-body is evolved from an        aerofoil as a body of revolution around the wing-body axis by an        angle less than 360 degrees. In this case, instead of being        closed, the duct will be partially open with a slot running        along its length. By making the angle greater than 180 degrees,        and preferably close to 360 degrees, the wing-body will remain        substantially annular so as to provide aerodynamic lift at any        angle of roll.

The annular air vehicles described above achieve significantimprovements in overall performance when measured across a broad rangeof whole vehicle criteria including lift to drag ratios, agility,stability, endurance, launch and recovery, take off or landing, power toweight ratios, fuel efficiency and resilience to aeroelastic loading.

The invention claimed is:
 1. An airborne vehicle having a wing-bodywhich defines a wing-body axis and appears substantially annular whenviewed along the wing-body axis, the interior of the annulus defining aduct which is open at both ends, wherein the wing-body appears sweptforward when viewed from a first viewing angle, and swept backward whenviewed from a second viewing angle at right angles to the first viewingangle wherein the wing-body has a leading edge with two or more noses,and a trailing edge with two or more tails.
 2. The vehicle of claim 1wherein the wing-body appears swept forward when viewed in plan, andswept backward when viewed in elevation.
 3. The vehicle of claim 1wherein the noses are rotationally offset in relation to the tails. 4.The vehicle of claim 1 wherein the wing-body has a leading edge and atrailing edge, and wherein at least part of the leading and/or trailingedge of the wing-body follows a substantially helical curve.
 5. Thevehicle of claim 1 wherein the wing-body has a projected planform areaS, and a maximum outer diameter B normal to the wing-body axis, andwherein the ratio B²/S is greater than 0.5.
 6. The vehicle of claim 1further comprising three or more undercarriage elements for providingstability during take-off and landing operations.
 7. The vehicle ofclaim 1 further comprising an energy source housed at least partiallyinside the wing-body.
 8. The vehicle of claim 1 wherein the wing-body isevolved from an aerofoil profile as a body of revolution around thewing-body axis.
 9. The vehicle of claim 8 wherein the aerofoil profilehas symmetrical upper and lower surfaces.
 10. The vehicle of claim 1wherein the wing-body has a leading edge which extends around acircumference of the wing-body, and wherein said leading edge appearsswept forward when viewed from a first viewing angle, and swept backwardwhen viewed from a second viewing angle at right angles to the firstviewing angle.
 11. The vehicle of claim 1 wherein the wing-body has atrailing edge which extends around a circumference of the wing-body, andwherein said trailing edge appears swept forward when viewed from afirst viewing angle, and swept backward when viewed from a secondviewing angle at right angles to the first viewing angle.
 12. Thevehicle of claim 10 wherein the wing-body has a trailing edge whichextends around a circumference of the wing-body, and wherein saidtrailing edge appears swept forward when viewed from a first viewingangle, and swept backward when viewed from a second viewing angle atright angles to the first viewing angle.
 13. The vehicle of claim 12wherein the trailing edge forms an identical shape to the leading edgeand is translated along the wing-body axis by a chord length of thewing-body.
 14. The vehicle of claim 1 wherein the wing-body has aleading edge which extends around a circumference of the wing-body, atrailing edge which extends around the circumference of the wing-body,and a mid-chord line between said leading and trailing edges, andwherein said mid-chord line appears swept forward when viewed from afirst viewing angle, and swept backward when viewed from a secondviewing angle at right angles to the first viewing angle.